Covalent triazine framework membrane as well as preparation method and application thereof

Abstract

The invention provides a covalent triazine framework membrane as well as a preparation method and application thereof. The covalent triazine framework membrane is prepared through a trimerization reaction of fluorine-containing aromatic nitrile monomers. The covalent triazine framework membrane disclosed by the invention is good in stability and flexibility and solvent-resistant, can be used in an organic solvent for a long time, and can be used for separating intersoluble organic liquids and fractionating crude oil.

Description

Technical Field

[0001] The invention belongs to the technical field of separation membrane materials, and in particular relates to a covalent triazine framework membrane and a preparation method and application thereof. Background Art

[0002] The hydrocarbons in crude oil are the main ingredients we use to make fossil fuels, plastics and polymers. Every day, up to 100 million barrels of crude oil are distilled in refineries around the world. The most common method used for crude oil distillation is distillation, of which the vast majority uses energy-intensive thermal distillation, which consumes more than 1,100 terawatt hours of energy each year, which is energy-intensive and costly.

[0003] Therefore, it is necessary to develop a green, low-carbon, and sustainable material that can be used for the separation of miscible organic liquids and crude oil fractionation. Summary of the invention

[0004] In view of the shortcomings of the prior art, the present invention aims to provide a covalent triazine framework membrane and a preparation method and application thereof, wherein the covalent triazine framework membrane is prepared by trimerization of fluorine-containing aromatic nitrile monomers. The covalent triazine framework membrane has good stability and flexibility and is solvent-resistant, can be used in organic solvents for a long time, can separate miscible organic liquids, and fractionate crude oil.

[0005] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0006] In a first aspect, the present invention provides a covalent triazine framework membrane, wherein the covalent triazine framework membrane is prepared by trimerization of fluorine-containing aromatic nitrile monomers.

[0007] In the present invention, the covalent triazine framework membrane is made of a fluorine-containing covalent triazine framework (CTFs) material, wherein the covalent triazine framework material is a new type of porous organic framework material formed by strongly aromatic triazine units connected by covalent bonds, and has extremely high porosity, good stability and flexibility.

[0008] The present invention obtains a covalent triazine framework membrane through a trimerization reaction of fluorine-containing aromatic nitrile monomers, as shown in the following reaction formula 1. The covalent triazine framework membrane is rich in fluorine element, which significantly improves the adsorption of organic liquids by the covalent triazine framework membrane, can separate miscible organic liquids, and can fractionate crude oil, thereby greatly increasing the flux of crude oil fractionation.

[0009]

[0010] in represents the continued connection of repeating units, and the structure of the repeating unit is shown in Formula 2 below.

[0011]

[0012] Where “-” represents the connection site.

[0013] Preferably, the fluorine-containing aromatic nitrile monomer includes 4,4'-((perfluoro-[1,1'-biphenyl]-4,4'-diyl)bis(oxyl))dibenzonitrile.

[0014] Preferably, the covalent triazine framework film is a covalent triazine framework nanofilm.

[0015] Preferably, the covalent triazine framework film has a thickness of 295-700 nm, for example, 295 nm, 300 nm, 320 nm, 350 nm, 400 nm, 450 nm, 500 nm, 550 nm, 600 nm, 650 nm or 700 nm.

[0016] In the present invention, the thickness of the covalent triazine framework membrane is 295-700nm. If the thickness is greater than 700nm, the permeation flux of the covalent triazine framework membrane is too low; if the thickness is less than 295nm, the strength of the covalent triazine framework membrane decreases and it is easily damaged during the preparation and separation process.

[0017] Preferably, the surface of the covalent triazine framework membrane has holes.

[0018] Preferably, the pore size of the covalent triazine framework membrane is 0.5-2 nm, for example, 0.5 nm, 0.8 nm, 1 nm, 1.1 nm, 1.2 nm, 1.3 nm, 1.4 nm, 1.5 nm, 1.6 nm, 1.7 nm, 1.8 nm or 2 nm.

[0019] In the present invention, the pore size of the covalent triazine framework membrane is 0.5-2nm. If the pore size is greater than 2nm, the component retention performance of the covalent triazine framework membrane decreases during crude oil separation; if the pore size is less than 0.5nm, the covalent triazine framework membrane has no permeation flux during crude oil component separation.

[0020] Preferably, the covalent triazine framework film is an annealed heat-treated covalent triazine framework film.

[0021] Preferably, the temperature of the annealing heat treatment is 300-450°C, for example, 300°C, 320°C, 340°C, 350°C, 370°C, 390°C, 400°C, 420°C, 430°C or 450°C, and more preferably 300-400°C.

[0022] In the present invention, the temperature of the annealing heat treatment is 300-450°C. Through annealing heat treatment at different temperatures, the content of fluorine in the covalent triazine framework membrane can be effectively controlled, thereby changing the surface properties and pore structure of the membrane material, achieving different degrees of interception of crude oil components, and achieving the effect of crude oil fractionation. If the temperature is too high, the carbon skeleton of the covalent triazine framework membrane will break and the interception effect will decrease; if the temperature is too low, the pore size of the covalent triazine framework membrane will not change after annealing, and the pore size will not be changed.

[0023] Preferably, the annealing heat treatment time is 2 to 3 hours, for example, 2 hours, 2.1 hours, 2.2 hours, 2.3 hours, 2.4 hours, 2.5 hours, 2.6 hours, 2.7 hours, 2.8 hours, 2.9 hours or 3 hours.

[0024] In a second aspect, the present invention provides a method for preparing the covalent triazine framework membrane as described in the first aspect, the preparation method comprising the following steps: mixing, spreading, and reacting fluorine-containing aromatic nitrile monomers and trifluoromethanesulfonic acid to obtain the covalent triazine framework membrane.

[0025] In the present invention, the trifluoromethanesulfonic acid functions to catalyze the trimerization reaction of fluorinated aromatic nitrile monomers and provide an acidic environment required for the reaction.

[0026] Preferably, the reaction further includes annealing heat treatment.

[0027] Preferably, the annealing heat treatment is performed in an inert gas atmosphere.

[0028] Preferably, the inert gas comprises argon.

[0029] Preferably, the annealing heat treatment is performed on an ITO glass sheet and annealed in a tube furnace.

[0030] Preferably, after the annealing heat treatment, the ITO glass sheet is further removed by etching with an etchant.

[0031] Preferably, the etchant comprises concentrated hydrochloric acid.

[0032] Preferably, the etching time is 24-48 hours, for example, 24 hours, 26 hours, 28 hours, 30 hours, 32 hours, 36 hours, 38 hours, 40 hours, 42 hours, 44 hours, 46 hours or 48 hours.

[0033] Preferably, in the mixture of the fluorinated aromatic nitrile monomer and trifluoromethanesulfonic acid, the concentration of the fluorinated aromatic nitrile monomer is 100-120 mg / mL, for example, 100 mg / mL, 102 mg / mL, 104 mg / mL, 106 mg / mL, 108 mg / mL, 110 mg / mL, 112 mg / mL, 114 mg / mL, 116 mg / mL, 118 mg / mL or 120 mg / mL, etc.

[0034] Preferably, the reaction temperature is 90-110°C, for example, 90°C, 92°C, 94°C, 96°C, 98°C, 100°C, 102°C, 104°C, 106°C, 108°C or 110°C, etc.

[0035] Preferably, the reaction time is 30 to 50 minutes, for example, 30 minutes, 32 minutes, 34 minutes, 36 minutes, 38 minutes, 40 minutes, 42 minutes, 44 minutes, 46 minutes, 48 ​​minutes or 50 minutes.

[0036] In a third aspect, the present invention provides a separation membrane, which comprises a substrate and the covalent triazine framework membrane as described in the first aspect.

[0037] In a fourth aspect, the present invention provides a use of the covalent triazine framework membrane as described in the first aspect in a miscible organic liquid separation material.

[0038] Preferably, the miscible organic liquid comprises crude oil.

[0039] In the present invention, membrane separation is a low-energy separation method and a possible alternative to thermal distillation for separating crude oil. Unlike thermal distillation, pressure-driven membrane separation technology uses the differences in the properties of hydrocarbons in crude oil (such as osmotic pressure, polarity, size or shape) for separation. It does not require the gasification of crude oil and has the advantages of energy saving and low carbon emissions. In theory, it will increase the energy efficiency of thermal distillation separation by 10 times.

[0040] In the present invention, the covalent triazine framework membrane can effectively control the content of fluorine in the covalent triazine framework membrane through annealing heat treatment at different temperatures, thereby changing the surface properties and pore structure of the covalent triazine framework membrane, achieving different degrees of interception of crude oil components, and achieving the effect of crude oil fractionation.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] The present invention obtains a covalent triazine framework membrane containing fluorine elements by trimerization of fluorine-containing aromatic nitrile monomers. The preparation method of the covalent triazine framework membrane is convenient and quick, and does not require complicated instruments and equipment; the covalent triazine framework membrane has a controllable membrane thickness, a thin thickness, good stability and flexibility, and solvent resistance, and can be used in organic solvents for a long time, and can be used for separation of miscible organic liquids, and fractionation of crude oil. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 A scanning electron microscope image of the surface of the covalent triazine framework film provided in Example 1;

[0044] Figure 2 A scanning electron microscope image of a cross section of the covalent triazine framework film provided in Example 1;

[0045] Figure 3 The covalent triazine framework membrane provided in Examples 1 to 4 is used to separate crude oil, and the color comparison diagram of the permeate obtained and the crude oil;

[0046] Figure 4 The covalent triazine framework membrane provided in Examples 1 to 4 is used to separate crude oil, and the gas chromatograms of the obtained permeate and crude oil are shown. DETAILED DESCRIPTION

[0047] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0048] Example 1

[0049] This embodiment provides a covalent triazine framework film and a preparation method thereof. The covalent triazine framework film is as shown in Figure 1 and Figure 2 , the preparation method of the covalent triazine framework membrane is as follows:

[0050] 100 mg of 4,4'-((perfluoro-[1,1'-biphenyl]-4,4'-diyl)bis(oxyl))dibenzonitrile was dissolved in 1 mL of trifluoromethanesulfonic acid and ultrasonically stirred to obtain a mixed solution. The mixed solution was evenly spread in a reaction container, and the reaction container was heated to 100° C. and kept warm for 30 minutes for polymerization reaction to form a film. The film was then transferred to an ITO glass sheet and the ITO glass sheet was removed by soaking in a concentrated hydrochloric acid etchant for 48 hours to obtain the covalent triazine framework film.

[0051] Example 2

[0052] This embodiment provides a covalent triazine framework film and a preparation method thereof. The preparation method of the covalent triazine framework film is as follows:

[0053] 100 mg of 4,4'-((perfluoro-[1,1'-biphenyl]-4,4'-diyl)bis(oxyl))dibenzonitrile was dissolved in 1 mL of trifluoromethanesulfonic acid and ultrasonically stirred to obtain a mixed solution. The mixed solution was evenly spread in a reaction container, and the reaction container was heated to 100° C. and kept warm for 30 minutes for polymerization reaction to form a film. The film was then transferred to an ITO glass sheet and placed in a tubular furnace for annealing heat treatment under an argon environment at a temperature of 300° C. for 2 hours. After cooling, the ITO glass sheet was removed by soaking in a concentrated hydrochloric acid etchant for 48 hours to obtain the covalent triazine framework film.

[0054] Example 3

[0055] This embodiment provides a covalent triazine framework film and a preparation method thereof, which is different from Embodiment 2 only in that the temperature of the annealing heat treatment is adjusted to 350° C., and other conditions are the same as those of Embodiment 2.

[0056] Example 4

[0057] This embodiment provides a covalent triazine framework film and a preparation method thereof, which is different from Embodiment 2 only in that the temperature of the annealing heat treatment is adjusted to 400° C., and other conditions are the same as those of Embodiment 2.

[0058] Example 5

[0059] This embodiment provides a covalent triazine framework film and a preparation method thereof. The preparation method of the covalent triazine framework film is as follows:

[0060] 110 mg of 4,4'-((perfluoro-[1,1'-biphenyl]-4,4'-diyl)bis(oxyl))dibenzonitrile was dissolved in 1 mL of trifluoromethanesulfonic acid and ultrasonically stirred to obtain a mixed solution. The mixed solution was evenly spread in a reaction container, and the reaction container was heated to 90° C. and the polymerization reaction was carried out for 40 minutes to form a film. The film was then transferred to an ITO glass sheet and placed in a tubular furnace for annealing heat treatment under an argon environment at a temperature of 300° C. for 2.5 hours. After cooling, the ITO glass sheet was removed by soaking in a concentrated hydrochloric acid etchant for 24 hours to obtain the covalent triazine framework film.

[0061] Example 6

[0062] This embodiment provides a covalent triazine framework film and a preparation method thereof. The preparation method of the covalent triazine framework film is as follows:

[0063] 120 mg of 4,4'-((perfluoro-[1,1'-biphenyl]-4,4'-diyl)bis(oxyl))dibenzonitrile was dissolved in 1 mL of trifluoromethanesulfonic acid and ultrasonically stirred to obtain a mixed solution. The mixed solution was evenly spread in a reaction container, and the reaction container was heated to 110° C. and kept warm for 50 minutes for polymerization reaction to form a film. The film was then transferred to an ITO glass sheet and placed in a tubular furnace for annealing heat treatment under an argon environment at a temperature of 400° C. for 3 hours. After cooling, the ITO glass sheet was removed by soaking in a concentrated hydrochloric acid etchant for 48 hours to obtain the covalent triazine framework film.

[0064] Example 7

[0065] This embodiment provides a covalent triazine framework film and a preparation method thereof, which is different from Embodiment 2 only in that the temperature of the annealing heat treatment is adjusted to 200° C., and other conditions are the same as those in Embodiment 2.

[0066] Example 8

[0067] This embodiment provides a covalent triazine framework film and a preparation method thereof, which is different from Embodiment 2 only in that the temperature of the annealing heat treatment is adjusted to 450° C., and other conditions are the same as those of Embodiment 2.

[0068] Example 9

[0069] This embodiment provides a covalent triazine framework membrane and a preparation method thereof, which is different from Embodiment 2 only in that the mass of the 4,4'-((perfluoro-[1,1'-biphenyl]-4,4'-diyl)bis(oxyl))dibenzonitrile is adjusted to 150 mg, and other conditions are the same as those in Embodiment 2.

[0070] Comparative Example 1

[0071] This comparative example provides a covalent triazine framework membrane and a preparation method thereof, which differs from Example 2 only in that 4,4'-((perfluoro-[1,1'-biphenyl]-4,4'-diyl)bis(oxyl))dibenzonitrile is replaced with an equal mass of [1,1':4',1"-terphenyl]-4,4"-dicarbonitrile, and other conditions are the same as those in Example 2.

[0072] The following performance tests were performed on the embodiments and comparative examples:

[0073] (1) Molecular carbon number of the permeate: The covalent triazine framework membrane provided in the embodiment and the comparative example was cleaned with deionized water, transferred to a polyethersulfone substrate and dried at room temperature, and then added to a pressure group, and crude oil (diluted heavy shale oil, mass ratio of toluene: heavy shale oil = 9:1) was added, and crude oil separation was performed at room temperature and 30 bar pressure. The molecular carbon number of the permeate was tested by observing the color of the permeate and gas chromatography.

[0074] The later the peak time of most high-intensity peaks in the above gas chromatogram and the darker the color of the permeate, the higher the molecular carbon number in the crude oil permeate and the higher the content of high-carbon number hydrocarbons; the earlier the peak time of most high-intensity peaks in the gas chromatogram and the lighter the color of the permeate, the lower the molecular carbon number in the crude oil permeate and the higher the content of low-carbon number hydrocarbons in the permeate.

[0075] If the color of the above-mentioned permeate is brownish yellow, the carbon number of the permeate molecules is considered to be high; if the color is light brownish yellow, the carbon number of the permeate molecules is considered to be relatively high; if the color is yellow, the carbon number of the permeate molecules is considered to be relatively low; if the color is light yellow, the carbon number of the permeate molecules is considered to be low; if the color is colorless, the carbon number of the permeate molecules is considered to be extremely low.

[0076] (2) Thickness of covalent triazine framework film: The thickness of the covalent triazine framework film was tested using a scanning electron microscope.

[0077] (3) Permeation flux of covalent triazine framework membrane: The permeation flux of the covalent triazine framework membrane was tested by regularly measuring the mass of the permeate sample flowing out of the pressure group.

[0078] The test results are shown in Table 1.

[0079] Table 1

[0080] Carbon number of permeate molecules Thickness(nm) <![CDATA[Permeation flux [L / (m 2 ·h·bar)]]]> Example 1 high 298 0.87 Example 2 Lower 298 0.38 Example 3 Low 298 0.13 Example 4 Very low 298 0.03 Example 5 Lower 500 0.22 Example 6 Very low 700 0.01 Example 7 high 298 0.85 Example 8 Higher 298 0.30 Example 9 — 1000 — Comparative Example 1 — 298 —

[0081] In Table 1, “—” means that the result was not measured.

[0082] According to the test results in Table 1, the covalent triazine framework membranes provided by Examples 1-8 are thin, stable and flexible, and can separate miscible organic liquids.

[0083] Comparison between Example 1 and Examples 2-4 shows that as the annealing temperature increases, the pore size of the covalent triazine framework membrane gradually decreases, resulting in a decrease in the permeation flux, while the degree of crude oil retention is enhanced. Figure 3 As shown, the color of crude oil is black, and the color of the obtained permeate gradually becomes lighter after the crude oil passes through the covalent triazine framework membranes provided in Examples 1-4. The permeate color of the crude oil in Example 1 is brownish yellow; the permeate color of the crude oil in Example 2 is yellow; the permeate color of the crude oil in Example 3 is light yellow; the permeate color of the crude oil in Example 4 is colorless. This is because the annealing temperature increases, the pore size of the covalent triazine framework membrane continues to decrease, resulting in a decrease in the content of polycyclic aromatic hydrocarbons in the permeate, and the carbon number of hydrocarbons continues to decrease, causing the permeate color to change.

[0084] like Figure 4 As shown, as the annealing temperature of the covalent triazine framework membrane provided in Examples 1-4 increases, the peak time of most high-intensity peaks is continuously shortened, indicating that the carbon number of hydrocarbons in the obtained permeate is continuously reduced.

[0085] The series of covalent triazine framework membranes prepared by annealing at different temperatures can retain crude oil to different degrees. The crude oil is separated in sequence using the covalent triazine framework membranes provided in Examples 1-4 to obtain hydrocarbon components with different carbon numbers, thereby achieving preliminary fractionation of crude oil.

[0086] Compared with Example 2, it can be seen that if the temperature of the annealing heat treatment is too low (Example 7), the performance of the covalent triazine framework membrane obtained is basically the same as that of the covalent triazine framework membrane that has not been annealed and heat treated, the membrane pore size is not reduced, the permeate flux becomes higher, the permeate still contains high-carbon hydrocarbons, and the retention effect is poor; it is proved that the annealing heat treatment temperature is 300-450°C, and the covalent triazine framework membrane prepared has better performance.

[0087] Compared with Example 2, it can be seen that if the annealing heat treatment temperature is too high (Example 8), the obtained covalent permeation flux becomes higher and the interception effect becomes worse. When the annealing heat treatment is performed at a temperature of ≥450°C, the interception effect begins to deteriorate. This is because the molecular skeleton of the triazine framework film begins to break and the pore size begins to increase.

[0088] Compared with Example 2, it can be seen that if the addition amount of fluorinated aromatic nitrile monomers is too high (Example 9) and the concentration of fluorinated aromatic nitrile monomers is high, the thickness of the obtained covalent triazine framework membrane becomes larger and the permeation flux decreases significantly, which proves that the covalent triazine framework membrane prepared by using fluorinated aromatic nitrile monomers in a specific concentration range has better performance.

[0089] Compared with Example 2, it can be seen that if the fluorine-containing aromatic nitrile monomer is replaced with a fluorine-free aromatic nitrile monomer (Comparative Example 1), there is no permeation flux and the separation of miscible organic liquids cannot be achieved.

[0090] The applicant declares that the present invention illustrates the process method of the present invention through the above-mentioned embodiments, but the present invention is not limited to the above-mentioned process steps, that is, it does not mean that the present invention must rely on the above-mentioned process steps to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of the raw materials selected by the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A covalent triazine framework film, characterized in that: The covalent triazine framework membrane is prepared by trimerization of fluorine-containing aromatic nitrile monomers.

2. The covalent triazine framework membrane according to claim 1, characterized in that: The fluorine-containing aromatic nitrile monomer includes 4,4'-((perfluoro-[1,1'-biphenyl]-4,4'-diyl)bis(oxyl))dibenzonitrile.

3. The covalent triazine frame membrane according to claim 1 or 2, characterized in that: The covalent triazine framework film is a covalent triazine framework nanofilm; Preferably, the covalent triazine framework film has a thickness of 295-700 nm.

4. The covalent triazine frame film according to any one of claims 1 to 3, characterized in that: The surface of the covalent triazine framework membrane has holes; Preferably, the pore size of the covalent triazine framework membrane is 0.5-2 nm.

5. The covalent triazine frame film according to any one of claims 1 to 4, characterized in that: The covalent triazine framework membrane is an annealed heat-treated covalent triazine framework membrane; Preferably, the temperature of the annealing heat treatment is 300-450°C; Preferably, the annealing heat treatment time is 2-3 hours.

6. A method for preparing a covalent triazine framework film as claimed in any one of claims 1 to 5, characterized in that: The preparation method comprises the following steps: mixing fluorine-containing aromatic nitrile monomers and trifluoromethanesulfonic acid, spreading, and reacting to obtain the covalent triazine framework membrane.

7. The preparation method according to claim 6, characterized in that: The reaction also includes annealing heat treatment; Preferably, the annealing heat treatment is performed in an inert gas atmosphere; Preferably, the inert gas comprises argon; Preferably, the annealing heat treatment is placed on an ITO glass sheet and annealed in a tube furnace; Preferably, after the annealing heat treatment, the ITO glass sheet is further removed by etching with an etchant; Preferably, the etchant comprises concentrated hydrochloric acid; Preferably, the etching time is 24-48 hours.

8. The preparation method according to claim 6 or 7, characterized in that: In the mixture of the fluorinated aromatic nitrile monomer and trifluoromethanesulfonic acid, the concentration of the fluorinated aromatic nitrile monomer is 100 to 120 mg / mL; Preferably, the reaction temperature is 90-110°C; Preferably, the reaction time is 30 to 50 minutes.

9. A separation membrane, characterized in that: The separation membrane comprises a substrate and the covalent triazine framework membrane according to any one of claims 1 to 5.

10. Use of the covalent triazine framework membrane according to any one of claims 1 to 5 in a miscible organic liquid separation material; Preferably, the miscible organic liquid comprises crude oil.

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